10 Range

Question 1

f

Specific air range?

Answer 1

The range through the air.
In nautial miles / Kg of fuel.

Question 2

Specific ground range?

Answer 2

The range across the ground.
In nautial miles / Kg of fuel.

Question 3

Fuel flow relationship in a jet and prop?

Answer 3

• In a jet fuel flow ~ thrust
• In a prop fuel flow ~ power

Question 4

What is the enroute phase?

Answer 4

1500ft after take off to 1500ft before landing.

Question 5

What is the SFC?

Answer 5

In a jet, this is the fuel flow per unit of thrust.
In a prop, this is the fuel flow per unit of power.

Question 6

When is SFC the best?

Answer 6

• Best is lowest.
• When the air temperature is low and the engine is running at its designed RPM (approx 90 to 95%)

Question 7

How can SAR be detailed in terms of SFC for a jet?

Answer 7

Fuel flow (jet) = SFC x Thrust Required)

SAR = TAS / Fuel Flow

SAR = TAS / (SFC x Thrust Required)

SAR = TAS / (SFC x Drag)

Question 8

Speed for maximum range of a jet?

Answer 8

1.32Vmd. At this speed a considerably greater TAS is achieved for only a small increase in drag. This is found using tangent to the drag curve.

Maximum range speed / Mach.

Question 9

Optimum altitude for maximum range in a turbojet?

Answer 9

Dictated by best engine SFC. The lowest SFC occurs at the point where the thrust required means that the engine core is running at optimum RPM. Above the optimum altitude SFC increases as engine has to run faster to produce the required thrust.

Generally better with altitude.

Question 10

What is the specific range for a prop driven aeroplane?

Answer 10

Fuel flow = Power required x specific fuel consumption (SFC)

Specific range (prop) = TAS / (SFC x Power Required(Drag))

Question 11

Speed for maximum range of a prop driven AC?

Answer 11

Vmd. Speed at which the ratio of TAS to power required in maximum.

Best range for a prop aircraft occurs at the tangent to PR which coincides with Vmd.

Question 12

Optimum altitude for maximum range on a piston engien AC?

Answer 12

SFC is best when RPM is lower and throttle is wide open.

At low altitudes this tends to produce too much thrust to fly at optimum range speed Vmd.

But as altitude increases, the avaliable power reduces. The optimum altitude occurs at the point where the engine is at full throttle height and producing just enough avaliable power required at Vmd.

Question 13

How does mass affect the range?

Answer 13

Heavy AC means an increased amount of induced drag. Therefore drag curve moves up and to the right.

The best range speed will need to increase.

Question 14

How does the CG affect the range?

Answer 14

An aft CG increases the maximum range. Less downforce required from the stabaliser.

Question 15

How does the config affect the range?

Answer 15

A greater drag inmeans that fuel consumtpion increases.

Question 16

Optimum altitude for a turbo prop?

Answer 16

The jet engine SFC is lowest at cold temperatures and at the design RPM.
Best at altitude where the optimum range speed can be maintained at the cruise RPM setting.

Question 17

Recommended range speed?

Answer 17

1.1Vmd
This is to increase the safety margin in te case of turbulance.

Question 18

Effect of altitude on raange summary?

Answer 18

Question 19

Effect of fuel burn on Vmd?

Answer 19

AC flying at the optimum altitude becomes lighter as it uses more fuel. Drag cuve moves left and down. (Lower optimum speed)

A lighter AC requires less thrust. So for engines to remain at constant ROM, altitude must increase.

**As flight progresses and weigth decreases, optimum altitude increases. **

Question 20

Step climb technique?

Answer 20

The goal is to increase range, by staying as close as operationally possible to the optimum altitude as the flight progresses.

Question 21

General effect of wind on range?

Answer 21

SAR is not effected by range as it depends on NAM/kg of fuel or TAS / fuel flow.

Headwind reduces SGR, and a tailwing increases the SGR. As it is dependant on ground speed.

Question 22

The effect of headwind on range for a jet?

Answer 22

The tangent at the curve must now be drawn not from the origin, but from a position corresponding to the headwind.

Therefore max range speed occurs at higher speed.
Overall range is reduced.

Question 23

The effect of tailwind on range for a jet?

Answer 23

The tangent to the curve orginates at a negative speed value equivalent to the velocity of the tailwind.

This results in a speed lower than 1.32 Vmd. Overall range is increased.

Question 24

Effect of wind on a prop driven AC?

Answer 24

Maximum SAR for a prop driven AC is at the tangent to the power required curve.

The best possible SGR is faster than Vmd for a headwind and slower than Vmd in a tailwind.

Question 25

What is the long range cruise speed (Mlrc)

Answer 25

In reality the operator may want the AC to fly faster Mmr to complete more flights in a given time.

This is 4% faster than the maximum range speed. This reduces the range by 1% which means that at Mlrc the AC achiveves 99% of the SAR archived at Mmr.

Question 26

Summarise Mlrc?

Answer 26

M_LRC > M_MR (long range cruise speed is faster than the maximum range speed, 1.32 V_MD), and

SR_LONG RANGE = 0.99 × SR_MAX RANGE

Question 27

What is the cost index?

Answer 27

cost index = Cost of time / cost of fuel.

Relating to cruise speeds from Mmr to Mmo. As the cost index increases Mecon increases.

Question 28

The effect of increasing mach number?

Answer 28

To minimise fuel burn, fly at Mmr or Mlrc.

The maximum cruise altitude will reduce, due to high speed buffet.

Question 29

Standard units for fuel consumption?

Answer 29

kg/eng/hr